CA1209116A

CA1209116A - Process for the complete replacement of particles in vessels

Info

Publication number: CA1209116A
Application number: CA000448881A
Authority: CA
Inventors: Gerrit J. Pronk
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1983-03-28
Filing date: 1984-03-05
Publication date: 1986-08-05
Also published as: GB2137112A; GB2137112B; GB8308473D0; JPS59183823A; US4502946A

Abstract

A B S T R A C T

PROCESS FOR THE COMPLETE REPLACEMENT OF
PARTICLES IN VESSELS
Process for the complete replacement under operating conditions of particles in a vessel provided with a feed inlet and, if desired, a separate particle inlet, a particle outlet and an effluent outlet, wherein part of a feed passing through the vessel during withdrawal of particles is by-passing the vessel when the particles still present in the vessel do not occupy more than 20%v of the volume initially occupied by particles and the feed to be processed is passed through the vessel before or during the addition of fresh particles.
The process is particularly suitable for the complete replacement under operating conditions of spent hydro-demetallization catalysts.

Description

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PRDCESS FOR THE CUMPIETE REPIA~DENT OF
pa ~3 VESSELS

The present inVentiGn relates to a process for the csmplete replacement of particles in a vessel. The present invention relates in particular to a process for the ccmplete replacement of catalyst particles used in the catalytic treatment of hydro-carbon oils such as demetallization, desulphurization and hydroconversion.
Since the feedstocks normally applied in oil processes, such as atmospheric and vacuum residues contain both metals such as nickel and vanadium as well as sulphur compounds, pre-treatments like (hydro)demetallization and (hydro)desulphur-ization are required to improve the quality of the feedstoc~
prior to further convexsion envisaged.
Catalysts play a vexy important role in hydroprocessing.
Proper fluid flow is desired to make full use of a catalyst's particular prcperties. The life of a catalyst in residue hydro-processing units is limited mainly due to the deposition of metals. m erefore, the catalyst has to ke replaced at certain intervals by a fresh chargef the spent charge either being discarded or regenerated in a separate operation. It will be clear that the replacement of catalysts is carried out preferably as late as possible and, m~rec~er, with a minimum down-time of the realtor concerned.
Quick catalyst replacement operations have been suggested ln the art (e.g. British Patent Specification Jo. 1,500,213) and can be applied successfully, but they have to be carried out whilst the reactor concerned is taken off-stream and has to be depressurized and cooled dcwn to ambient temperature.
On-stream replacement of catalyst charges can be carried out in n~ving-bed or bunker reactors (e.g. as described in British Patent specification No. 1,331,935~. m e replacement occurs gradually and can be carried out continuously or periodically in bunker reactors equipped for mass-flow behaviour of the catalyst charge. Mass-flcw behaviour of the solids present is normally obtained by resting the catalyst bed(s) on one or more conical supports having in the centre a catalyst outlet duct leading to a sluicing system. Since catalyst replacement is carried out on-stream, the addition of fresh catalyst also requires the presence of a sluicing system.
It may be necessary for various reasons, however, to replace the complete charge of a catalyst or catalyst/carrier mixture preset in a reactor.whilst maintaining the reactor under cperatir.g conditions. This can ye accomplished success-fully when a number of reactors in series is operated provided the reactor to be refilled with catalyst is temporarily dis-ccnnected frcm the supply and removal lines for the hydrocarbon feeds and effluents ~e.g. British Patent Specification No.

2,014,058).
However, in carrying out this replacement operation, the main feed to the reactor has to be stGpped and additional hot purge gas (e.g. hydrogen at a temperature of about 350C~ has to be purged through the reactor in order to prevent temperature excursions. me consequence of the use of a purge gas is, hcwever, the presence of a complicated valve handling around the reactor(s) concerned together with an additional hot purge gas flow circuit in size and throughput ccmparable with the recycle gas flow normally employed.
It has ncw been found that complete replacement under operating conditions of particles in vessels provided with inlet(s) and outlets can be accamplished without the need of complicated valve ha~dlin~ and without the presence of an additional purge gas circuit when the flow of feed through the vessel is controlled carefu11y during the catalyst withdrawal procedure.
m e present inventicn thus relates to a process for the complete replacement under operating conditions of particles in a vessel provided with a feed inlet and, if desired, a separate ~LZC~

particle inlet a particle outlet and an effluent outlet wherein part of a feed passing through the vessel Turing withdrawal of particles is by-passing the vessel when the particles still present in the vessel do not occupy more than 20%v of the volume initially occupied by particles and the feed to be processed is passed thrcugh tlhe vessel before or during the addition of fresh catalyst.
The process according to the present invention is carried out preferably in such a way that part of the feed passing through the vessel during withdrawal of particles is by-passing the vessel when the particles still present in the vessel do not occupy more than 10%v of the volume initially occupied by particles.
The process accordlng to the invention is carried out conveniently when part of the feed by-passing the vessel during withdrawal of particles, in particular spent catalyst particles, is fed to one or mDre further vessels under operating conditions, in particular under similar operating conditions as the vessel being replenished with (catalyst3 particles.
In practice, spcnt catalysts used in hydroprocessi~g residual material such as (hydro)demet~llization, (hydro)desulphur-ization and hydroconversion, can now be ~letely replaced. Thy main advantage is that the feed to be processed travels through the vessel which catalyst charge is being withdrawn during a substantial amount of the total catalyst withdrawal procedure so that temperature excursions are kept under control or even prevented (the feed passing through being an effective cooling mEdium) sin oe the amount of catalyst present is reduced continu-ously during the withdrawal.
The process of by-passing the reactor at the final stage of the catalyst withdra~lal procedure has the important advantage that the pressure drop over the reactor is gradually reduced as far as possible, thus minimizing pr ssure disturbances in the process. In particular, the undesired effect of pinning (i.e. the formation of a stagnant zone in which the particles - ~2~

do no longer move adjacent to screens forming the particle/fluid separation section) is controlledO
Feeds which can be used in the process according to the invention ccmprise, for instance, hydrocarbon oils, especially hydrocarbon oils which are to ye subjected to a demetallization and/or desulphurization treatment As examples may be mentioned crude oil, oil frcm which the volatile products are remcved (topped crude oil), oil from which light products are removed by distiilation at atmospheric pressure (long residue), shale oils as well as oils obtained from tar sands. Residual fractions as described hereinabove are preferred feeds.
The particles to be replaced can be, for instance, spent or partly spent demetallization or deslllphurization catalysts.
Demet~llization catalysts usually consist of oxidic carriers on 15 which one or more metals or metal cG.I~Gunds with hydrogenation activity may be deposited. Reference is made to catalysts as disclosed in Dutch patent specification 7309387 containing at least one metal of the grcup consisting of nickel and cobalt, at least one metal of the group consisting of molybdenum, vanadium and tungsten, supported on a carrier and fulfilling in fresh condition the following requirements:
1) p/d > 3.5 0.02v, where p represents the specific average pore diameter in nm, d represents the specific average particle diameter in mm and v is the percentage of the total pore volume consisting of pores having a diameter above 100 nm, 2) the total pore volume is above 0~40 ml/g,

3) v is below 50 and

4) the specific surface area is above 100 mZ/g; in case the catalyst has such a p and d that the quotient p/d is abcve 3.5-O.O~v, but at most 10-0.15v, the fresh catalyst must fulfil the following additional requirements:
a) the nitrogen pore volume is above 0.60 ml/g, b) the specific surface area is above 150 m2/g and c3 p is above 5 nm.

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m e values to be used for p, d, v, the total pore volume, the nitrogen pore volume and the specific surface area must be determined as described in the afore-mentioned Dutch patent specification. Alumina, silica and silica-alumina are very suitable as carriers. Preference is given to carriers completely or substantially consisting of silica.
Catalysts as described in Dutcn patent specification 7316396 containing 0.1-15 parts by weight of the metal cGmbi-nation nic~el-vanadium per 100 parts by weight of a silica carrier, having a loss on ignition, determined under standard conditions, of less than 0.5% by weight are very suitable. Alsc catalysts described in Dutch patent specification 7412155 having a pore volume, present in pores having a diameter above 50 nm, of at least 0.2 ml/g and obtained by the nodulizing technique can be used conveniently. Silica on which no metals with hydro-genation activitv have been deposited, as described in Dutch patent spec'fication 7607552, can be used when the hydrocarbon oil to be demetallized has a high metal content.
The hydrotreat~ent, in particul æ the hydrod~metallization of hydrocarbon oils (normally at least 80 vol.% being in the liquid state) is conveniently carried out by passing th3m together with hydrogen in downward ~;rection over the appropriate catalyst at a temperature between 300 and 4S0C (preferably between 350 and 425C), a total pressure between 75 and 250 bar (preferably between 100 and 200 bar), a hydrogen partial pressure between 35 and 200 bar (preferably between 50 and 175 her), a space velocity of 0.1-25 parts by volume of fresh feed per part by volume of catalyst per hour and a hydrogen/feed ratio of 500 2000 (preferably 750-1500) Nl of H2/kg of feed.
The hydrogen required for the hydrotreatment may be a hydrogen~containing gas stream, such as a reformer off-gas stream, or a nainly pure hydrogen. The hydrogen-containing gases prefPrably contain at least 60% by volume of hydrogen. The de~etallization need of course not be complete and a quantity of metal may still be present in the treated product.

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It may be attractive to subject the resultant demetallized hydrocarbon oil to a hydrodesulphurization treatment and it is advantagecus to carry out the demet llization and desulphurization in or.e continuous treatment without intermediate isolation and/or purification of the demetallized hydrocarbon oil and of the hydrogen-containing qas egging available.
For the hydrcdesulphurization of heavy hydrocarbon fractions, such as residual fractions, specific catalysts are kncwn which can be used for a long tLme without replacement or regeneration o the catalyst being necessary as a result of deposition of metals, coke and high-mDlecular ccmponents (such as resins, polyarcmatics and asphaltenes) from the feed. Reference is made to catalysts described in Dutch patent specification 7010427.
The particles of said catalysts have a pore volume above 0.30 ml/g, of which pore volume less than 10% is present in pores having a diameter above lO0 nm and the catalyst particles have a specific pore diameter expressed in nm from 7.5 x d0 9 to 17 x d0 9, in which d represents the specific particle diameter in mm.
Catalysts which can be suitzbly employed include sulphur-resistant catalysts co~prisin~ one or more of Group VIB, VIIB
and/or VIII metals, their sulphides or oxides deFosited on an amorphous refractory inorganic Q~ide of Group II, III or rv elements, or a cc~position of said inorganic oxides. Catalysts containing nickel or ccbalt together with molybdenum are particularly suitable. Very suitable carriers are silica, silica-alumina and in particular alumina.
The hydrcdesulphurization is carried out under the usual conditic~s~ The demetallized hydrocarbon oil or a hydrocarbon oil hazing a very low metal content to be desulphurized together with fresh hydroyen and/or hydrogen already present is very suitably passed in downward direction over the catalyst at a temperature between 350 and 425C, a total pressure between lO0 and 250 bar, a hydrogen partial pressure between 50 and 175 bar, 3~2@~ Pi a space velocity of 0.1-20 parts by volume of fresh feed per part by volume of initial catalyst per hour and a hydrogen/feed ratio of 500~1500 Nl H2/kg of feed.
The (catalyst) particles to be replaced cGmpletely will S normally be present in apparatuses suitable for (catalytic) processes, in particular in reactors having an external or internal geometry which ensures mass flow of the (catalyst) particles. Reactors which can be used convenient_y in residue hydroprocessing are so-called bunker or moving-bed reactors.
The catalyst bed(s) in the reactor rest on conical supports having in the centre a catalyst outlet duct as will be described hereinafterO
Preferred apparatuses which can be used in the catalytic treatment of hydrocarbons wherein a complete catalyst replacement is required ccmprise reactors which contain at least one tray in addition to supporting means for one or more catalyst beds, which supporting means are permeable to liquid and gas and Dmpermeable to catalyst particles and in which the supporting means are at least partly in the shape of a conical surface of a truncated cone and which supporting.means are attached to the wall of the reactor and are prc,vided with a dcwnward-directed opening permeable to catalyst particles and in which beneath each supporting m ans a tray is located which is permeable to liquid and gas and imFermeaDle to catalyst particles which tray has an opening which is permeable to catalyst particles. The supportlng means æe positioned preferably m such a way that the acute angle formed by a descriptive line of the conical surface(s) and the axis of the reactor is from 35 45.
The pertaining Figure 1 is a schematic drawing of an 3Q apparatus which can ye used for caxrying out the replacement according to the present invention. It will be clear that the ccmplete replacement of a catalyst charge will be carried out in one reac~uDr at the time. The other reactors depicted in Figure 1 illustrate that the complete replacement is par of a multi-12~

reactor system as is preferably employed in large scale operations.
Referring to Figure 1, 100, 200 and 300 are three reactors which under normal operating conditions (when no (catalyst) particles are replaced) are provided with the appropriate (catalyst particles up to the levels 101, 201 and 301, respec-tively. The feed, for instance a heavy hydrocarbon oil to be hydro-demetallized, is supplied via line 1 to the top of reactor 100 and ls led over the appropriate catalyst particles (shaded area) supported by supportinq means 102 and 103 having downward-directed openings for the passage of catalyst. The stream of treated feed leaves reactor 100 by passing through the liquid and gas permeable guide-face 103 and enters reactor 200 via line 3 and enters reactor 300 via line 4. m e effluent leaving reactor 300 is removed via line 5 fox further processing such as distillation and, if desired, partial recycle of top and/or bottom fractions to earlier stages in the process.
(Catalyst) particles can be supplied via line 2 but under normal operation this will not take place since the valves 105, 205 and 305 are closed. It should be noted that it may not be necessary to equip the reactors with individual supply lines when the (catalyst particles can be supplied via a connection (not shown) to the feed supply line 1. On the other hand, it may be useful to employ a separate (catalyst) supply line in case different layers of (catalyst) particles are required to fill up the alloted (catalyst) particles space. During normal operation the feed is directly introduced Lnto the first reactor - and through the first reactor to the next - since the by-pass vaLves A, B and C are closed.
By opening valve 104, preferably a rotary valve, the unloading of (catalyst) paxticles from reactor` 100 commences (whilst the main process flow continues to flow through reactor 100) and spent (catalyst) particles are removed via line 6 and may be discarded or directed to a regeneration unit, preferably after removal of effluent. When the unloading of the catalyst ~26~

has proceeded to the stage that it occupies not more than 20%
of the volume initially occupied by catalyst (indicated as a percentage of the shaded area in the similar reactor 200, e.g.
as indicated by broken line 106), valve A is opened which allows the main process flow to proceed directly to reactor 200. Valve 104 remains opened until the remainder cf the (catalyst) particles has been withdrawn from the reactor. Thereafter valve 104 is closed and by-pass valve A is closed so that the process flow enters reactor 200 again via line 3, i.e. after having passed through reactor 100 totally devoid of catalyst.
The reloading of reactor 100 is carried out whilst the process flow is continued through reactor 100 by either opening valve 105 to allcw for the intrcduction of (catalyst) particles (either as such, or, preferably, in a slurry in a suitable liquid such as a hydrocarbon), or by transporting the (catalyst) particles in the main process flow through line 1. When the level of the catalyst bed has reached the appropriate level (indicated as 101), the (catalyst) charge of reactor 200 can be replaced by carrying out a similar operation. Valves A, B and C
are closed when valve 204 is cpened to allow withdrawal of catalyst from reactor 200. When the unloading of reactor 200 has proceeded to the stage that the catalyst does not occupy more than 20% of the volume initially occupied by catalyst, valve B
is opened which allows the main process flcw to proceed directly to reactor 300.
Valve 204 remains open until the catalyst has been with-drawn totally frcm reactor 200. Thereafter, valve 204 is closed and by-pass valve B is closed so that the process flow leaves again reactor 200 via the liquid and gas permeable guide-face 203 and enters again reactor 300 via line 4. Reloading of the catalyst charge is carried out whilst the main process flow continues thrcugh reactor 200 either by opening valve 205 or by introducing the catalyst) particles directly with the feed Replacement of the (catalyst) charge of any further reac-tors (only one reactor (300) depicted in Figure 1) can be carried out in the same manner as described hereinabove.
m e mvention is illustrated by means of the follow mg EYE ple.
EX~PLE
In an apparatus as described in Figure 1, the reactors 100, 200 and 300 are filled with a demetallization catalyst. Said catalyst contains 0.6% by weight of nickel (as oxlde) and 1.9~
by weight of vanadium (as oxide) cn silica as carrier and has a specific average pore diameter of 13.6 nm, a specific average particle diameter of 2.2 mm, a specific surface area of 262 m2/g and a pore volume of 0.78 ml/g, of which pore volume 0.3%
consists of pores having a diameter above 100 nm. A residue of a mineral oil having under reaction conditions a specific heat of 2kJ/kg/C is subsequently passed throuah the reactors 100, 200 and 300 at a rate of 10 kg/s, a 300-inlet temperature of 400C, together with hydrcger. at a gas velocity of 1 Nm3/kg of feed, which gas under reaction conditions has a specific heat of 25 kJ/hmol/C and a heat of reaction of 12kJ/m3 of catalyst/s.
When under normal operating conditiGns as described herein-akove a temperature increase of 10C is aeceptable for a reaction proceeding at the given inlet temperature, the volume available for catalyst particles equals 26 m3. In order to 25 prevent a temperature increase of more than 10C when the catalyst is removed under operating conditions, 90% of the feed (i.e. 90% of the gas and 90% of the liquid) by-passes the reactor when the catalyst still present in the reactor equals 2.6 m3, i.e. not more than 10%v of the total volume available for catalyst. When under otherwise similar conditions a tEmperature increase of 20C is acceptable, the by-pass of the reactor can be in operation when the remaining catalyst particles occupy 2 m3 of the total volume available for catalyst particles, i.e.
not mDre than 20%v of the total volume available for catalyst 35 particles.

Claims

C L A I M S

1. Process for the complete replacement under operating conditions of particles in a vessel provided with a feed inlet and, if desired, a separate particle inlet, a particle outlet and an effluent outlet, characterized in that part of a feed passing through the vessel during withdrawal of particles is by-passing the vessel when the particles still present in the vessel do not occupy more than 20%v of the volume initially occupied by particles and the feed to be processed is passed through the vessel before or during the addition of fresh particles.

2. Process according to claim 1, characterized in that part of the feed passing through the vessel during withdrawal of particles is by-passing the vessel when the particles still present in the vessel do not occupy bore than 10%v of the volume initially occupied by particles.

3. Process according to claim 1 or 2, characterized in that part of the feed by-passing the vessel during withdrawal of particles is fed to one or more further vessels under operating conditions.

4. Process according to claim 1, characterized in that the catalyst charge of a (hydro)demetallization reactor is replaced.

5. Process according to claim 1, characterized in that the catalyst charge of a hydrodesulphurization reactor is replaced.

6. Process according to claim 4, characterized in that the catalyst charge is withdrawn from a vessel containing at least one tray and supporting means for one or more catalyst beds, which supporting means is (are) permeable to liquid and gas and impermeable to catalyst particles and in which the supporting means is (are) at least partly in the shape of a conical surface of a truncated cone and is (are) attached to the wall of the vessel and is (are) provided with a downward-directed opening permeable to catalyst particles, and in which beneath each supporting means a tray is located which is permeable to liquid and gas and impermeable to catalyst particles, which tray has an opening which is permeable to catalyst particles.

7. Process according to claim 4, characterized in that a demetallization catalyst is replaced containing at least one metal of the group consisting of nickel and cobalt, at least one metal of the group consisting of molybdenum, vanadium and tungsten, supported on a carrier and fulfilling in fresh condition the following requirements:
1) p/d > 3.5-0.02v, where p represents the specific average pore diameter in nm, d represents the specific average particle diameter in mm and v is the percentage of the total pore volume consisting of pores having a diameter above 100 nm, 2) the total pore volume is above 0.40 ml/g, 3) v is below 50 and 4) the specific surface area is above 100 m2/g; in case the catalyst has such a p and d that the quotient p/d is above 3.5-0.02v, but at most 10-0.15v, the fresh catalyst must fulfil the following additional requirements:
a) the nitrogen pore volume is above 0.60 ml/g, b) the specific surface area is above 150 m2/g and c) p is above 5 nm.

8. Process according to claim 5, characterized in that a (hydro)desulphurization catalyst charge is replaced which comprises a sulphur-resistant catalyst comprising one or more of Groups VIB, VIIB and/or VIII metals, their sulphides and/or oxides deposited on an amorphous refractory inorganic oxide of Group II, III or IV elements, or compositions of said inorganic oxides.

9. Process according to any one of claims 4, 6 and 7, charac-terized in that the replacement is carried out at a temperature between 300 and 450°C, a total pressure between 75 and 250 bar, a hydrogen partial pressure between 35 and 200 bar, a space velocity of 0.1-25 parts by volume of fresh feed per part by volume of initial catalyst per hour and a hydrogen/feed ratio of 500-2000 N1 H2/kg of feed.

10. Process according to any one of claims 5, 6 and 8, characterized in that the replacement is carried out at a tempera-ture between 350 and 425°C, a total pressure between 100 and 250 bar, a hydrogen partial pressure between 50 and 175 bar, a space velocity of 0.1-20 parts by volume of fresh feed per part by volume of initial catalyst per hour and a hydrogen/feed ratio of 500-1500 N1 H2/kg of feed.